Paving structure



Jan. 12, 1965 R. J. SCHMIDT PAVING STRUCTURE Filed March 1, 1965 IN VE NTOR ROBERT J. SCHMIDT ATTORN EYS 3,165,036 PAWNG STRUQTURE I Robert J. Schmidt, El (Ierrito, (Jalifi, assignor to :Cah-

fornia Research Corporation, San Francisco, Cahh, a corporation of Eelaware Filed Mar. 1, 1963, Ser. No. 263,377 14 (Jlaims. (Cl. 94-7) The present invention relates to composite-type pavement structures and method of preparing the same, and particularly to such structures which can be applied as overlays for strengthening, resurfacing, and protecting various pavements and road surfaces. More particularly yet, it relates to laminated overlays serving to reinforce pavements subjected to extensive wear due to heavy trafiic, to minimize skidding, to provide a warning to motoristsapproaching dangerous portions of a road, such as curves and intersections, and to protect pavements from damage which may be occasioned by water and spilled solvents and liquids.

It has been suggested already to employ plastic overlays to reinforce and-to protect Portland cement concrete (PCC), asphalt-concrete (AC), and other like pavements apt to become damaged by cracking under the continued impact of intensive daily traffic load, this cracking being aggravated by the adverse action of water and atmospheric moisture and by spillage of oil, grease and motor fuels.

Accordingly, various plastic materials, e.g., alkyd resins, epoxy resins and asphalt, have been applied as seal coats or overlays on different pavement surfaces whenever the particular circumstances seemed to justify their use. For instance, to reduce the risk of skidding of motor vehicles on curves and at intersections, particularly in wet weather, plastic overlays, specifically asphalt overlays, containing sand and/or other suitable, comparatively fine, particulate solid materials have been applied onto the pavement. lastic overlays, colored to attract attention and to give a visual warning to the approaching motorist, have also been tried in various locations.

Likewise, rumble strips in the form of pavement overlays prepared with asphalt and placed in sequence across a trafiic lane and in which large aggregate is bonded in the plastic to form a jagged, sawtooth-like surface, have been proposed to give an audible warning to slow down to motorists approaching a hazard by giving rise to a higher noise level and by vibrating the vehicles.

Plastic overlays have also been considered and employed as seal coats on pavements built of Portland cement concrete (FCC) and asphalt-concrete (AC) to minimize the damage likely to be suffered by the pavement surface from the adverse action of oil, grease, and fuel. However, the actual experience has pointed out that not every plastic material can be employed satisfactorily as a pavement overlay, although such an overlay may appear initially to be an effective anti-skid coating, a rumble strip or a seal coat.

Asphalts which have been proposed for use in such overlays lack strength, tend to soften up and to melt in warm weather with loss of aggregate, and, upon expansion and contraction with the change of ambient temperature, form little cracks and crevices through which water penetrates and then freezes at lower temperatures, damaging the underlying road base. Furthermore, asphalts are not impervious to petroleum fluids, such as oil and gasoline.

Many of the synthetic thermoplastic resins, although easily applied to the pavement surface, lack satisfactory adhesion and tend to flow and to deform under load and are very vulnerable to attack by solvents.

Thermosetting resins, owing to their high tensile, fiexural, impact and adhesion strengths, high distortion temperatures and softening points, resistance to water, hydrocarbons, etc., as a general rule, produce good surface cover (overlays) for Portland cement concrete, asphaltconcrete, and other rigid-base pavements. However, their acceptance by the trade has been hindered so far by several serious drawbacks attendant totheir utilization, namely, necessity of axspecial preparation of the underlying surface before applying the resin, precise control and timing of its application, and, particularly, eventual occurrence of cracks in the underlying pavement upon setting, due to the differences between the coefiicient of expansion or" the thermosetting resin and that of the underlying pavement base, particularly if this base is formed by asphalt-concrete. The resin, once it has set, forms a very strong bond with the underlying pavement which will not yield when subjected to thermal stresses. The

result is cracking and eventual disintegration of the base,

since ground water and rain Water seep through the cracks, and, upon alternate .freezing and thawing, further promote the breaking of the pavement.

The present invention is directed at enabling successful utilization of thermosetting resins in pavement overlays, wherein'the resin is present as one or as several layers of a laminated paving structure and in which the aforementioned tendency toward cracking and deteriora tion is substantially eliminated. This is achieved by the introduction of a layer of a thermoplastic bituminous material, such as an asphalt, between the underlying pavementand the surface coating of the resin. In the laminated pavement structure thus constructed, when this structure is subjected to the conditions of thermal stress, such as occur during the cure of the overlay and with subsequent variations of ambient temperature, the layer of bituminous material acts as a slip-plane and the rigid resin surface moves independently of the pavement structure below. Therefore, the underlying pavement does not crack and does not allow water to penetrate therethrough, while the resin layer minimizes the likelihood of injury to the pavement by contact with other solvents that may be spilled on the top surface of the overlay.

- ture of the invention can be represented as shown in FIG. 1 of the drawing attached to this specification. In FIG. 1, A is the pavement base of an asphalt-concrete, Portland cement concrete, or the like. B is a layer of asphalt acting as the slip-plane and applied onto A either as hot liquid asphalt or as an emulsion of asphalt in water. This layer B is followed by a layer C consisting of mineral aggregate, such as stone, stone chips, gravel or sand, to provide an adequate barrier between the asphalt layer B and the layer of resin D which is applied next onto the aggregate layer C, for instance, by

Patented Jan. 12,, 1965 spraying This barrier is desirable because an unduly long direct contact with asphalt during the resin cure may interfere with the setting (hardening) of certain thermosetting resins. As a matter of fact, such a barrier will be interposed between the top thermosetting resin layer and the slip-plane layer of any thermoplastic bi- Luminous material, soluble in carbon disulfide and containing free-radical inhibitors, and, consequently, apt to inhibit the cure of thermosetting resins which set (harden) by a free radical mechanism, as'typified by the hardening of: unsaturated polyester resins. The thermoplastic materials which, by virtue of their bituminous character and their content of free-radical inhibitors, particularly tend to inhibit theresin cure, are various asphalts, pitches and tars, adequately rigid at normal temperatures and under normal conditions of stress, but otherwise capable of deformation when subjected to heat and pressure. The

' asphalts may be steam-refined, solvent-refined, air-blown,

- order to prevent slipperiness and to impart a particular desired, characteristic to the resin surface, it is topped by a layer of a finely particulate solid, such as sand, sawdust, cut colored fibers, coloring-sand mixtures, etc. as shown by E in FIG. 1.

Also, several successive layers of resin or alternating layers of resin and sand may be employed, depending on the ultimately intended use of the overlay, whether as a seal coat on a-road, on a runway of an airport, on

the surface of a wharf, or a bridge, and the like.

One advantage of applying these overlays is that no complicated precleaning of the original pavement surface is required. In other words,no necessity exists for resorting to a sequence of sweeping, steam cleaning, and, finally, etching the surface with dilute alkali or acid. It suifices tosweep the pavement surface, whether concrete (FCC) or asphalt-concrete (AC), of all loose material, whereupon the asphalt layer may be immediately applied thereto either. as a hot asphalt or as an asphalt emulsion (anionic or cationic). The stone aggregate is applied immediately thereafter. If asphalt has been applied as anemulsion, the application of resin is postponed until the emulsion is suificiently dehydrated. Otherwise, the resin may be immediately sprayed on the surface of the aggregate.

' .For certain specialized applications of these overlays, such as rumble strips, and armor coats, an intermediate choke layer of sand or other suitable finer aggregate, will precede the application of resin. The resin is then applied in a sufiicient amount to bind firmly the surface of the choke (sand fill) and any protruding coarser aggregate surfaces by one continuous coating. Thereafter, a final application of a finely particulate solid material, such as sand, cut fibers, saw dust, iron oxide, etc. will produce the desired outside surface. Before opening the road to tra'llic, excess of sand or like topping material is simply swept off. in general, the asphalt is applied at a rate ot'about 0.1 to 0.5 gallon per square yard of the paved surface; for coarse textured overlay structures rates from about 0.25 to about 0.5 gallon of asphalt per square yard are preferred. On Portland cement concrete and in overlays prepared with case of asphalt emulsions, the rate is based on the actual asphalt content thereof. Any suitable mineral aggregate conventionally used for paving work may be employed in in the preparation of the overlays in accordance with the invention. The size of the individual particles (sto es of the aggregate, their nature and texture are not critical and are chosen in accordance with the local conditions and requirements of each particular case. However, in the construction of rumble strips," which will be described later on, the aggregate to be embedded the asphalt atop the underlying pavement base generally varies in size from 1 /2" to /s, meaning that the majority of the stones in such aggregate has linear dimensions lying between these limits. Accordingly, in such cases, the choke layer is formed by an aggregate which is finer in size than the first embedded aggregate.

A particular embodiment of the invention relates to the preparation of the so-called rumble strips. They are placed atop a pavement in locations adjacent to dangerous intersections and curves, so that the tires of and, consequently, the motor vehicle itself in riding over these strips become subjected to a greater degree of vibration than in riding over the re ular pavement surface of the same road. This vibration is translated both into a tactile and an audible warning as the vehicle approaches the danger, causing the driver to slow down.

A schematic representation of suci rumble strip overlay paving structure is shown in PK}. 2. of the draw ing. In FIG. 2, the numeral 1 designates the underlying pavement base. A layer of asphalt 2 is applied at the rate from approximately 0.10 to about 0.50 gallon per square yard onto this base surface. The rate figures are based on undiluted asphalt so that, if an asphalt emulsion (anionic or cationic) is employed, the rate figures refer to the actual asphalt content of this emulsion.

A course of coarse stone aggregate, from 1 /2" to is in size and one stone in thickness, is then embedded into the asphalt which is employed in an amount sufficient to bind these stones but not to submerge them. This stone course is designated 3 in FIG. 2. A "choke layer of sand or other suitable liner mineral aggregate, designated by 4, is then applied to fill the interstices of the individual stones of layer 3 and to form a more or less impervious barrier between the asphalt and the coating of a thermosetting resin which is applied following the choking step. The purpose of the choke layer is to forestall the contact of the resin with the asphalt (or any other thermoplastic bituminous material, when it is used in lieu of asphalt). As mentioned before, when this contact is prolonged, it may inhibit the cure of certain thermosetting resins, probably owing to the presence of free-radical inhibitors, such as phenolic constituents in the asphalt. Before spraying on the resin, excess of sand is swept off. The resin is then applied (in one or several successive layers) using any suitable application technique. it binds the individual particles of the choke layer and coats the protruding portions of the coarse stone aggregate, forming a continuous rigid surface film 5. To impart the desired non-slippery texture to the outer surface of the rumble strip overlay, sand is applied onto the resin coating before it becomes hardened. Upon setting, the excess sand may be swept oil. if desired, several applications of resin and sand, successively or simultaneously, may be applied onto the original resin coating.

The following observations confirmed the necessity of providing, according to the invention, a choke layer of finer stone aggregate to separate substantially completely the bituminous thermoplastic slip-plane from the layer of polyester resin, when using for this slip-plane a tar which tends to inhibit the resin cure.

A coating emulsion of coal tar available on the market under the trademark Colfix was employed to coat a 7" X 14 x 2" specimen of asphalt concrete pavement.

When the emulsion has broken (set), a thin layer of a high-impact, flexible polyester resin of the same kind as in the tests describedhereinbefore where asphalt was used in the slip-plane, was applied to the tar-coated surface of the specimen. However, after three Weeks, the surface was found to have remained tacky, indicating the failure of the resin to cure satisfactorily. Increasing the thickness of the resin layer did not provide a more satisfactory coating. In fact, after three weeks, on being peeled back with a knife, the polyester-coal tar interface was again found to have remained tacky.

On the other hand, when a similar specimen of asphalt concrete pavement coated with the same coal tar emulsion received first an application of one-half inch aggregate and No. 10 mesh sand, and then was given an application of the aforementioned polyester resin, the resin became completely cured within 1 /2 hours without any indication of tackiness, bond failure between the resin layer and the concrete base, or cracks in the resin coating. It was evident that the cure of the resin has not been at all inhibited, and that the choke layer served as an effective physical barrier separating the coal tar and the resin. In armor coat-type overlays, that is, in overlays which are used to protect portions of road surfaces exposed to heavy trafiic loads, the aggregate embedded in the asphalt layer applied onto the original pavement surface need not be as coarse as in the case of rumble strips. Since in armor coats the top surface is to be rather smooth and the aim is not to produce vibration and rumbling noise, aggregate stone sizes from about 1" to about /1." are found satisfactory. The quantity and the rate of application of the asphalt correspondingly may also be somewhat lower. For choking, a suitable aggregate (sand orgrits) of a finer size will be used, also followed by a layer (or layers) of thermosetting resin and by a final seal-coat (or coats) of resin and sand. Preferably, several courses of resin and fine aggregate will be applied to produce a firm, non-skid protective overlay.

On the other hand, where a thin, lightweight A" or less) overlay is desired, whether to provide a solventresistant surface and to prevent ravelling or to reduce the risk of skidding, an even finer stone aggregate, from about /5" to about /8", will be embedded in the asphalt layer, the asphalt being applied at a rate from approximately 0.10 to 0.50 gallon per square yard, usually from about 0.10 to 0.15 gallon per square yard.

A schematic representation of an armor coat or a lightweight overlay is shown in FIG. 3 of the drawing.

In this figure, the symbol a designates the original pavement surface; b designates the asphalt slip-plane layer; 0, designates the coarse aggregate; a, the finer aggregate or sand choke; e, the coating of resin; and sand or grits held .in resin in a firm, fine-textured seal-coat surface.

In all of these different embodiments of laminated overlays of the invention, in accordance with requirements of eachparticular case, several coats of resin may be successfully'applied before the final resin-sand application, or several alternating layers of resin and sand may be employed to protect the underlying pavement structure. In all instances, clean, dry aggregate of more or less the same size should be employed. For better non-skid efiect, stones with high polishing resistance or special anti-skid materials, such as crushed granite chips, sharp crushed sand, aluminum oxide, carborundum and the like are to be preferred. v

As to the actual practical construction of overlays in accordance with the invention, any suitable and readily available equipment may be employed for the purpose.

The asphalt is applied as any conventional seal coat,

and the stone aggregate, particularly when preparing -rumble strips is embedded by light pneumatic-tire rolling, to avoid the risk of grinding or breaking the stones. Fine aggregates, such as chips or sand, are spread 6 in any suitable effective manner, for instance, from tailgate mobile spreaders. I

In applying the resin, where areas to be covered by an overlay are small, the operation may be done by hand; otherwise, any suitable equipment, such as travelling spray-oar or twin spray-bars with multiple heads mounted on a trailer may be employed.

As pointed out before, any thermosetting resin, such as phenolic resins, epoxy resins, unsaturated polyester resins and the like, may be employed. Unsaturated polyester resins prepared by reacting polyhydricalcohols or phenols with polybasic (preferably aromatic) acids, in which at least a part of the alcohol or of the acid reactant contains a polymerizable unsaturated double bond, are

among the preferred thermosetting resins.

As examples of polyhydric alcohols or phenols which can be. used to prepare the resins, there may be mentioned: ethylene glycol, propylene glycol, diethylene glycol, di-

propylene glycol, triethylene glycol, 1,3-butanediol, neopentyl glycol, and bis-phenol A.

Suitable polybasic acids are: phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, and tetrachlorophthalic anhydride, benzene dicarboxylic acids being particularly preferred.

The unsaturated carboxylic acids, which are usually employed to modify the polyestersand which may be blended with the aforementioned polybasic acids are dicarboxylic acids and include maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic acid, and the like.

The unsaturated polyesters prepared from the aforementioned acids and alcohols are mixed with a polymerizable unsaturated cross-linking agent, for instance, styrene, vinyl toluene or vinyl pyrrolidone, and polymerization is then induced by the addition of a free radical initiator (catalyst) and of an accelerator to the mixture. The actual blending and proportioning of the reactants and reaction promoters may be carried out in any suitable manner.

Among the various thermosetting resins, those derived by cross-linking (for instance, using styrene) unsaturated polyester resins which have been prepared by reacting with a dihydric alcohol (a glycol) a phthalic acid, or an anhydride thereof in admixture with an unsaturated carboxylic acid, such as maleic, are particularly suitable for the preparation of the laminated paving structures of.

the present invention.

Polyester resins derived from isophthalic acid and containing an unsaturated double bond which has been provided by substituting a portion of the isophthalic acid by an unsaturated acid, such as maleic anhydride, are preferred for the preparation of overlays inaccordance with the invention. These resins and their preparation have been described in the prior art. They are non-toxic, cure well between about 40 and about F. and possess a viscosity which permits spraying and mixing them readily at ambienttemperatures. durable covering, impervious to solvents and provide ex cellent protection to the underlying pavement against cracking, water seepage and deterioration, if applied as a part of'a laminated structure according to the invention.

A number of overlays were prepared and applied on existing pavements, in accordance with the technique described hereinbefore, and then tested under severe traffic conditions.

In one test series of such overlay applications near a busy boulevard intersection, the asphalt layer was produced by applying it at a rateof 0.4 gallon per square yard on an asphalt concrete pavement. Altogether, six rumble strips were placed in succession on the asphalt concrete portion of the road followed by two rumble strips on the adjacent Portland cement concrete bridge deck. Finally, one anti-skid strip was placed at the heavily acid, hexachloroendomethylenetetrahydrophthalic On setting, they form a strong asphalt was 85-100 penetration asphalt applied hot. [resin was an isophthalic acid unsaturated polyester resin prepared by reacting a diethylene glycolethylene glycol mixture (in a 4: 1 mol ratio) with a mixture of isophthalicfumar'ic acids (in a 3:4 mol ratio). The cross-linking agent wasstyrene (40% by weight). The rates of application of asphalt, resin, coarse aggregate and sand were as described hereinabove.

The resin, upon being cured, was characterized as follows:

Barcol hardness 33-36 Flexural strength, psi 18,000 Impact strength in ft.-lb./in. 68 Heat distortion temperature in F 174 After two months of service, all of the aforementioned seven overlay strips were found to be in excellent condition and showed no loss of stone (ravelling), and no cracking of the underlying pavement. n approaching the rumble strips, the background noise level by the drivers ear, in a car with the windows closed, on the original uncoated (without overlay) pavement was measured to be 94 decibels. As the car crossed each strip, the

noise level increased to an average of 104 decibels for a fraction of a second. This heightening of the noise level together with the vibration of the steering wheel was repeated and perceived each time a rumble strip was traversed before coming to the intersection, thus giving a clearly perceptible tactile and audible warning to the driver. In addition, even though many drivers suddenly applied the brakes on approaching the intersection over the rumble strips, the structure or these overlays showed no damage upon inspection.

In another test, an anti-skid verlay was applied on an asphalt concrete pavement on a heavily traveled truck. road in .a petroleum refinery. The asphalt layer which served as a slip plane in this overlay structure was applied as a cationic asphalt-in-water emulsion (260-300 penetration asphalt), after sweeping the pavement. Stone chips /8" size) -were laid into this asphalt emulsion layer, and the emulsion left to become thoroughly dehydrated. This application'was followed by a choke layer of afiner aggregate (sand) to cover the asphalt, and the excess of sand was swept off. Thereupon, the same isophthalic 'aci'd polyester resin as that described in the preceding series of tests was applied on the sand choke and the protruding tips of the coarser aggregate chips. This'resin application was followed by another application of'resin and then by a final surfacing treatment with sand.

pavement. ,7

Finally, in an extensive series of tests, a number of' rumble strips and anti'lskid overlays were placed on a wide, heavily used automobile and truck thoroughfare. Inapp-lying theseoverlays, one-half of the road pavement surface (two lanes leading north) wasdivided into three longitudinal strips, and the asphalt was applied to each at a different application rate. For rumble strips, the overlay section nearest the curb received an asphalt coating at a rate of 0.25 gal; per sq. yd. The center section received 0.4 gal. of asphalt per sq. yd., and the third section ending at the center ine of the highway received 0.25 gal. per sq. yd.. For anti-skid strips, the corresponding rates of asphalt were 015, 6.25 and 8.15 gal. per sq.

yd. In this way, cars traveling in the two northbound lanes had their wheels on each side traversing a surface coating laid on a diiierent thickness of the asphalt slip plane layer. Hot asphalt of 8540 3 penetration was employed in forming the slip plane layer.

The asphalt-coated sections of the pavement were embedded with different aggregates. in rumble strips, three kinds of aggregates were used, ranging from about to about 1" in average size as the first course; next, a choke layer" of a finer aggregate (e.g., N0. 8 mesh sand); and, finally, a fine sand layer for surfacing at the top. For anti-skid strips, the coarse aggregate to be embedded in the asphalt consisted of stone chips from about /4 to about /1" in size, the choke layer" consisted of No. 8 grits, and the same material was employed to top the surface.

Four different formulations of polyester resins were employed:

AA reaction product of diethylene glycolcthylene glycol (4:1 mol ratio) and isophthalic-fumaric acids (3:4 mol ratio);

BA reaction product of propylene glycol and isophthalic-rnaleic acids (1:1 rncl ratio);

CA polyester resin similar to that described under (A) with phthalic anhydride being substituted for isophthalic acid;

DA polyester resin similar to that described under (B) with phthalic anhydride again being substituted for isophthalic acid.

Formulations (A) and (B) were blended with 40% styrene, while formulations (C) and (D) were blended with 30% styrene, as the cross-linking agent.

in all instances, methyl ethyl ketone peroxide was employed as the catalyst and cobalt naphthenate as the accelerator for the reaction.

In this particular test series a trailer-mounted traveling spray bar with two spray guns was employed to apply the polyester resin. First, the polyester and the accelerator and the polyester and the catalyst were manually proportioned and blended into two separate mixtures, and each mixture was then fed through a separate line to the spray gun. One gun sprayed the resin blended with the accelerator, and the other sprayed the resin blended with the catalyst, and the two streams met on the pavement surface. Concentration of the catalyst and the accelerator was so adujsted as to give a setting time of about 30 minutes.

ltogether, l2 transverse sections were prepared with the aggregate embedded in the asphalt slip-plane atop the original asphalt concrete (AC) pavement. From 4 to 6 different applications of the four resin formulations, previously described, were applied to these transverse sections, using different application rates. In several applications, calcium carbonate filler was dispersed in proportions varying from 20 to 50% in the resin. In certain controlled sections of the pavement, no resin was employed for the construction of the overlay.

After two months, all the overlays on the road surface subjected to testing were examined. All of these overlay structnres constructed in accordance with the invention, namely, comprising the asphalt slip layer and the resin coating, were found to be in a satisfactory condition. No cracks could be observed in the underlying original pavement. In test strips laid without the application of polyester resin cover, stones were lost from the asphalt bed, irrespective of the rate employed in applying the asphalt. No loss of stone was noted in the resin-coated overlays.

The follo g tabulation offers an idea of the extensiveat which the resin formulation has been applied in gallons per square yard of the surface; and the third column gives the number of test sections (overlays).

Table 1 Application No. of Test Resin Rate (GaL/ Sections Sq. Yd.)

13 B (40% CaCOs) B (60% CaCOa)" g (60% OaOOzL--- G CaOOs) O CaCOaL. g (60% CaCOx)" D D (40% 0800a)-.-. D (60% C3003) From the foregoing description of the invention and of the representative results of a number of tests in actual road service, it is clearly apparent that a new and improved composite overlay paving structure is provided by the invention. The structure is not only resistant to Water, petroleum and other solvents but, in addition, and contrary to the experience of the prior art and practice, eliminates the tendency towards cracking in the pavement surface underlying such overlays. Because of their high tensile strength, these overlay structures are particularly applicable for the construction and reinforce- 45 ment of flexible pavements subjected to high trafiic loads and wear.

Specifically, the application of these overlays in the construction of rumble strips, owing to the sawtooth nature of the surface of these strips, facilitates Water drainage and reduces the wiping action imposed on the automobile tire treads in wet weather.

Furthermore, these laminated structures,.when employed as lightweight overlays, reduce the dead load of the paving structure and enable minimizing of grade changes, while providing a durable surface coating of the pavement surface. Because of the exceptional strength of the hardened thermosetting resin surface, particularly when using isophthalic acid resins, the overlays prepared therewith appear to be exceedingly suitable for use in airstrips for jet aircraft, Where jet blasts are known to cause rapid deterioration of the conventional surfaces of air strips.

The paving structures suitable for use in armor-coats, rumble strips, and anti-skid overlays in accordance with the present invention may be constructed directly on the job by known paving techniques.

However, where the magnitude of the construction job and/or other circumstances do warrant, one need not resort to a large-scale work of paving or resurfacing by applying a slip-plane of bituminous material on the pavement base, following it by a layer of coarse stone aggregate, then by a choke layer of a finer stone aggregate, and finally by a layer of a thermosetting resin. 7

Slabs of the paving structure of a suitable specified thickness and size may be prepared (precast) instead at a manufacturing plant and transported to the job to be placed and fitted as needed in the particular area to be paved.

The present application is a continuation-in-part of ap-.

plication Serial No. 73,813, filed by the same applicant on December 5, 1960, now abandoned.

I claim:

1. The process for preparing a paving structure, which comprises applying a layer of a thermoplastic bituminous material onto a rigid base; partially embedding a layer of coarse stone aggregate into said layer of bituminous thermoplastic material; introducing into the interstices of said coarse stone aggregate layer a finer stone aggregate, so that the coarse stone aggregate and the finer stone aggregate together cover completely the surface of the layer of bituminous material; binding the exposed portion of said coarse stone aggregate and the finer stone aggregate layer with a layer of a thermosetting resin; and topping said resin with a layer of a fine particulate solid material.

2. The process as defined in claim 1 wherein said bituminous material is an asphalt.

3. A process as defined in claim 1 wherein said bituminous material is a tar.

4. The process as defined in claim 1, in which said thermosetting resin is an unsaturated polyester resin.

5. A process as defined in claim 1 wherein said thermosetting resin is a benzene dicarboxylic acid-unsaturated carboxylic acid polyester resin.

6. A process as defined in claim 1 wherein said thermosetting resin is an isophthalic acid-unsaturated carboxylic acid polyester resin.

7. A paving structure comprising:

(a) a rigid base;

(b) a slip-plane layer of a bituminous thermoplastic material upon said base;

(0) embedded therein a layer of coarse stone aggre gate;

(d) .a finer stone aggregate covering the surface of the layer of bituminous material and leaving exposed the top portion of the coarse stone aggregate, so that the coarse stone aggregate and the finer stone aggregate together cover completely the surface of the layer of bituminous material;

(e) a layer of a thermosetting resin upon said finer stone aggregate and said exposed coarse stone aggregate, said resin penetrating and binding said finer aggregate into a cement-like surface and firmly adhering to the portion of the coarse stone aggregate protruding above said surface; and

(f) a top layer of sand adhering to said resin layer.

8. A paving structure as defined ,in claim 7 wherein said bituminous material is an asphalt.

9. A paving structure as defined in claim 7 wherein said bituminous material is a tar.

10. A paving structure as defined in claim 7 wherein said thermosetting resin is an unsaturated polyester resin.

11. A paving-structure as defined in claim. 7 wherein said resin is an aromatic acid-unsaturated carboxylic acid polyester resin.

12. A paving structure as defined in claim 7 wherein said resin is a benzene dicarboxylic acid-unsaturated carboxylic acid polyester resin.

13. A rumble-strip paving structure comprising a rigid base, a slip-plane layer of asphalt upon said base, embedded in said layer of asphalt a layer of coarse stone aggregate ranging in size from 1 /2" to a layer of a finer stone aggregate to cover the surface of the asphalt and to leave exposed the top portion of the coarse stone aggregate, so that the coarse stone aggregate and the finer stone aggregate together cover completely the surface of the asphalt layer, a layer of a thermosetting resin upon said finer s one aggregate and said exposed portien of 14. A rumble-strip paving structure as defined in claim the coarse stone aggregate to bind the finer aggregate into 13, wherein said finer stene aggregate severing the asphalt a ce t-like u f d to dh fi l t 1 ti fi f surface Wiih the coarse stone aggregate embedded iherein 1 coarse a aggregage protruding abcve i su facg is sand, and the fine pariiculate solid material atop the and a top layer of a fine particulate solid material adher- 5 layer 13 also Sand- 'ing to the resin layer. No references cited 

1. THE PROCESS FOR PREPARING A PAVING STRUCTURE, WHICH COMPRISES APPLYING A LAYER OF A THERMOPLASTIC BITUMINOUS MATERIAL ONTO A RIGID BASE; PARTIALLY EMBEDDING A LAYER OF COARSE STONE AGGREGATE INTOSAID LAYER OF BITUMINOUS THERMOPLASTIC MATERIAL; INTRODUCING INTO THE INTERSTICES OF SAID COARSE STONE AGGREGATE LAYER A FINER STONE AGGREGATE, SO THAT THE COARSE STONE AGGREGATE AND THE FINER STONE AGGREGATE TOGETHER COVER COMPLETELY THE SURFACE OF THE LAYER OF BITUMINOUS MATERIAL; BINDING THE EXPOSED PORTION OF SAID COARSE STONE AGGREGATE AND THE FINER STONE AGGREGATE LAYER WITH A LAYER OF A THERMOSETTING RESIN; AND TOPPING SAID RESIN WITH A LAYER OF A FINE PARTICULATE SOLID MATERIAL. 